Coaxial transmission lines



Sept. 26, 1967 D. N. SEWELL COAXIAL TRANSMISSION LINES 2 Sheets-Sheet 1 Filed June 3, 1965 Sept. 26, 1967 D. N. SEWELL COAXIAL TRANSMISSION LINES Filed June 3, 1965 2 Sheets-Sheet 2 United States Patent This invention relates to coaxial transmission lines and, more particularly, to support arrangements for maintaining two tubular conductors in spaced coaxial relation and to methods and apparatus for manufacturing such support arrangements.

Conventional forms of coaxial transmission lines that comprise a tubular inner conductor disposed within a tubular outer conductor employ dielectric spacing devices to maintain the coaxial relation of the two tubular conductors. A conventional type of spacing device is a disc that is disposed in an undercut section of the inner conductor or is otherwise suitably secured so that substantially the entire outer periphery of the disc engages the inner surface of the outer conductor. Such a spacing device introduces a substantial amount of dielectric material in the line and compensation must be provided to maintain the desired electrical characteristics of the transmission line. Another conventional type of spacing device is a dielectric pin which involves less dielectric material and hence less compensation than the disc devicev Conventional assembly techniques of such a spacing device involve the drilling of holes in the inner conductor into which ceramic or polytetrafluoroethylene pins are inserted and then securing the pins in place by clamping arrangements inside the inner conductor or by placing sleeves over the exposed ends of the pins, in order to position each pin with an equal amount exposed on either side of the inner conductor. A typical pin arrangement is in groups of three offset from one another radially by 120 at intervals along the inner conductor as prescribed by mechanical support requirements and electrical wave length of the signals to be carried in the line. The necessary electrical compensation for such pins is typically provided by additional holes drilled in the inner conductor near a single pin or a group of pins, or by forming depressions near the pins in either the inner or outer conductors. It has also been proposed to compensate each pin assembly individually, but heretofore such compensation has been expensive to achieve and it has been difficult to appropriately lock the pins in position on the inner conductor with such compensation.

Accordingly, it is an object of this invention to provide a novel and improved coaxial transmission line.

Another object of the invention is to provide a new and improved dielectric support structure assembly for a coaxial transmission line.

A further object of the invention is to provide a novel and improved coaxial transmission line employing pins as dielectric support elements.

Still another object of the invention is to provide novel and improved methods for manufacturing coaxial transmission lines.

A further object of the invention is to provide novel and improved apparatus for securing a dielectric support member in a coaxial transmission line structure.

A coaxial line constructed in accordance with the invention includes an inner conductor having secured thereto a plurality of radially projecting dielectric support pins of deformable material. The pins preferably are angularly offset from one another and are spaced axially along the length of the inner conductor. Each pin is dis- 3,344,370 Patented Sept. 26, 1967 posed in two diametrically opposed apertures in the inner conductor and extends through the inner conductor with equal portions projecting from either side thereof. Each aperture includes asmoothly curved toroidal compensation surface that bends inwardly of the conductor wall and terminates in a plurality of prongs, at least one of which adjacent each aperture is forced into the deformable pin material so that that pin is positively locked in position. The inner conductor with pins secured thereto is then inserted into the outer conductor to form the coaxial line.

In manufacturing the inner conductor-support pin assembly, the inner conductor is first pierced in a controlled manner to simultaneously form the smoothly curved toroidal compensating surface and the inwardly projecting tabs of desired orientation extending from that surface at two diametrically opposed points. A dielectric pin of suitable deformable material, such as polytetrafluoroethylene, is inserted through the two diametrically opposed openings and properly positioned so that the portions projecting from either side of the inner conductor are equal. One or more tabs formed on the inside of the inner conductor adjacent each opening are then forced towards and into the dielectric pin material to secure the pin in position. Preferably, the tabs have spearpoints 'which are firmly embedded in the pin. This structure provides simple yet secure locking of the pin against axial movement in either direction at a point not exposed to high frequency electrical forces.

The apparatus for forming the tabs and locking those tabs in position into the dielectric pin, in the preferred embodiment, includes a two-component support arranged for positioning within the inner conductor; a cooperating outer alignment structure which includes guides for piercing elements and which also provides an alignment structure for properly positioning the dielectric pin relative to the inner conductor; and two opposed piercing elements with cooperating drive. The two components of the support are axially separable from a mating surface which is bridged by two aperture defining bores, each of which has a smoothly curved entrance. Initially, the inner conductor is positioned between the inner support and the cooperating alignment structure and the two piercing elements are driven from opposite directions towards one another as guided by the alignment structure intothe aperture defining bores to pierce the inner conductor at two diametrically opposed points and form two annular smoothly curved compensation surfaces, the configuration of which is determined by the entrance surfaces of the bores. Each compensation surface terminates in a plurality of inwardly projecting tabs each of which preferably terminates in a spearpoint. After the compensation surfaces and the tabs have been formed, the inner support components are separated so that they clear the formed tabs and permit rotation and axial movement of the inner conductor.

The inner support also carries a set of opposed tab clinching elements. One element is mounted on one component of the support and the cooperating element is mounted on the other component so that they are movable axially toward one another. The cooperating alignment structure includes a curved support surface located at a predetermined radius with respect to the axis of the inner conductor. After the inner conductor has been rotated to clear the aperture defining bores, it is moved axially so that a dielectric pin may be inserted through the formed conductor openings and positioned on the support surface in proper position. The pin is aligned with the clinching elements and then they are moved towards oneanother to act against the tabs and force their spearpoints into the dielectric pin from opposite side thereof and at each opening to securely lock the pin relative to the inner conductor.

The conductor with the locked pin secured therein is then moved to another desired position relative to the support and cooperating alignment structure. Other pins are similarly locked to the inner conductor along the length thereof at differing angular positions and then the assembly of inner conductor and dielectric support pins is inserted into the outer conductor to provide a coaxial transmission line with the locked dielectric pins supporting and maintaining the desired coaxial relationship.

The resulting transmission line has its inner and outer conductors accurately supported in coaxial relation by a support structure that employs a minimum of dielectric material so that a minimum amount of compensation is required, which compensation was formed during the assembly of the support pins. The pins are locked in place in a manner which does not increase the weight of the coaxial line. A further advantage is that no potential sources of contamination such as soldering or welding fluxes are employed in the manufacture of the support structure for the coaxial line.

Other objects, features and advantages will be seen as the following description of a particular embodiment of the invention progresses, in conjunction with the drawings, in which:

FIG, 1 is a side view, partially in section, of a coaxial electrical transmission line constructed in accordance with the invention;

FIG. 2 is a sectional view of the transmission line taken along line 22 of FIG. 1;

FIG. 3 is a perspective view of the inner conductor with a series of dielectric pins secured thereto;

FIG. 4 is a diagrammatic view of apparatus for securing a dielectric pin to the inner conductor;

FIG. 5 is an end view of the apparatus shown in FIG. 4 showing details of the piercing device;

FIG. 6 is a perspective view of the inner support employed in the apparatus shown in FIG. 4;

FIGS. 7-10 are diagrammatic views illustrating the series of steps practices by the apparatus shown in FIGS. 46 for piercing the inner conductor and securing the dielectric pin in place (FIG. 10 being along the line 10--10 of FIG. 13);

FIG. 11 is a sectional view of the inner support and conductor positioned thereon taken along the line 1111 of FIG. 7 with the cooperating alignment structure omitted;

FIG. 12 is a sectional view similar to FIG. 11 showing the inner conductor in rotated position after the apertures have been formed; and

FIG. 13 is a sectional view similar to FIGS. 11 and 12 showing the position of the tubular conductor during the tab crimping operation to lock the dielectric pin in place.

With reference to FIG. 1, there is shown a coaxial transmission :line having a tubular outer conductor 10 and a tubular inner conductor 12. Formed in the tubular inner conductor 12 are pairs of diametrically opposed openings 14 with tabs or prongs 16 that are bent inwardly from openings 14 from a uniform compensating radius 17.

A pin 18 of a deformable dielectric material such as a polytetrafiuoroethylene is inserted through two diametrically opposed openings in position so that portions 20, 22 that are equal in length protrude from either side of inner conductor 12. The spearpoints 24 of two opposed tabs 16 at each opening 14 are forced into the deformable dielectric material of pin 18, so that these spearpoints project into the dielectric material and prevent movement of pin 18 in either direction so that the pin 18 is securely locked relative to the inner conductor 12.. Additional pins are similarly secured to the inner conductor 12 along the length thereof at angularly offset positions such as in groups of three each offset 120. The assembly of dielectric pins 18 on the center conductor 12 are inserted into the tubular outer conductor 10 in the position shown in FIGS. 1 and 2 and in that position the two inner conductors are disposed in coaxial relation with a minimal amount of dielectric material in the transmission line and the electrical compensation required due to the dielectric support element is provided by the aperture radii 17.

The apparatus for securing the dielectric pins 18 to the inner conductor 12 is indicated in FIGS. 4 and 5. An operating station 30 is positioned at one end of the assembly on support 32 and a control station 34 is spaced at a suitable distance, such as thirty feet from station 30 on support 36. Intermediate supports 38 are provided as necessary. The operating station 30 and control station 34 are connected by three concentrically disposed coupling members 42, 44, and 46 with annular space provided between coupling members 42 and 44 in which the tubular inner conductor 12 is received.

At the operating station 30, there is positioned an alignment structure 50 which includes two diametrically opposed guide channels 52, 54 and a curved support surface 56. This alignment structure is suitably secured to coupling member 42.

Two component inner support 60 is secured to coupling members 44 and 46, body component 62 being secured to coupling member 44 and end component 64 being secured to coupling member 46. Two crimping tools 66, 68 are secured to the body component 62. and project axially beyond the end component 64 as best indicated in FIG. 6. Each crimping tool has a crimping element 70 having a sharp point surface thereon. Formed on end component 64 opposite each crimping element 70 is a cooperating crimping projection '72. Disposed between and bridging the mating surfaces of the body component 62 and the end component 64 is a forming channel 74 which has a smoothly curved entrance surface 76. In addition, the periphery of end component 64 is cut away at diametrically opposed points 78.

Also disposed at the operating station 30 is a piercing structure generally indicated in FIG. 5. This structure is mounted on a framework secured to the support structure 32 and includes an upstanding frame member 82 having pivotally secured thereto two arms 84, 86 which are disposed above and below the alignment structure 50. The two arms, at their ends opposite the pivot connections, are coupled together by a suitable operating mechanism indicated as a pneumatic cylinder 90 having a piston rod 92, cylinder 90 being coupled to lower arm 86 and the end of the piston rod 92 being coupled to the upper operating arm 84. Pivotally connected to each operating arm 84, 86 at an intermediate point and in alignment with one another are two piercing pins 94, 96 which are normally disposed in the guide channels 52, 54 in structure 50. The arm and cylinder assembly rests on support 98.

At the control station 34, there is a second control cylinder 100 having a piston 102 therein. The cylinder 100 is connected to both coupling members 42 and 44 so that they are fixed in alignment while the piston 102 is connected to coupling member 46. Thus, the coupling members 42 and 44 maintain the structure 50 and the body component 62 of the inner support 60 in alignment while the end component 64 of inner support 60 may be moved in an axial direction relative to the body component 62 and the outer structure 50.

Operation of this apparatus will be best understood with reference to FIGS. 7-13 shownng a series of views at operating station 30. In the position shown in FIG. 7, the tubular inner conductor 12 is positioned between the outer structure 50 and the inner support structure 60. The spacing between the two structures is such that the tube 12 can be relatively freely rotated. In the first operation, the piercing members 94 and 96 are moved towards one another by control cylinder 90 to drive them down through the wall of the inner conductor 12. It will be noted that each piercing element 94, 96 has four fiat surfaces disposed at 90 to one another so that four prongs 16 tend to be formed, each having a spearpoint 24, two in line of axial direction of the conductor and two perpendicular thereto. As the piercing elements 94, 96 are forced down through the metal of conductor 12, they force that metal down over the compensation determining radius 76, providing a smooth transition from the cylindrical surface of the conductor 12, and then separate the metal to form the prongs 16. This piercing and prong forming operation is indicated in FIGS. 7 and 8.

After the prongs have been formed, the piercing elements 94 and 96 are withdrawn. The end component 64 of the inner support 60 is then moved away from the body component 62 by energization of control cylinder 100 to move the piston 102 to the left as indicated in FIG. 4. This operation provides sufficient space for the formed prongs 16 to clear the bore walls 74 and then the conductor 12 may be rotated approximately 30 relative to the mandrel structures 50, 60 to the position shown in FIG. 12. In this position, the prongs 16 are aligned with the apertures 78 in the end component 64 and permit the conductor 12 to be moved axially out (to the left as indicated in FIG. 4). The conductor is moved approximately one inch to the position shown in FIG. 9 so that the formed apertures 14 are aligned with sup port 56. In this position, a dielectric pin 18 is inserted through the formed openings as indicated in FIG. 9 so that one end is seated on support 56. This support is of uniform curvature so that as conductor 12 is rotated the pin continues to ride on the positioning support 56 without shift in axial position. The conductor 12 is then rotated to the position shown in FIG. 13 so that the formed prongs 16 are disposed between the crimping teeth 70 and 72. The cylinder 100 is then actuated to move the piston 102 to the left to force the crimping teeth towards one another and to crimp the prongs into the dielectric pin 18 as indicated in FIG. 10.

After the prongs 16 have been crimped into the pin 18 so that their spearpoints 24 are firmly embedded in the pin 18 and prevent its movement in either direction, the two components of the inner support are then moved to release the crimping force and the conductor with pin 18 secured thereon may be rotated and moved axially to the desired position for insertion of the next dielectric support pin.

Thus, the apparatus enables the assembly of the improved dielectric support arrangement in a simple operation. The support arrangement employs a minimum amount of material and appropriate electric-a1 compensation is automatically formed in a manner which minimizes the reduction of the power handling capabilities of the coaxial line.

While a particular embodiment has been shown and described, various modifications thereof will be obvious to those skilled in the art. For example, the adjustability of the two components of the inner support may be obtained through use of a threaded interconnection between the two components and/ or rotation of one component relative to the other. Similarly, the clinching of the prongs into the dielectric pin may be obtained by rotation of one clinching element towards another. Therefore, it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

What is claimed is:

1. A coaxial electrical transmission line comprising a tubular outer conductor;

a tubular inner conductor coaxially disposed within said outer conductor;

said inner conductor having a plurality of pairs of opposed aligned apertures therein;

the wall of each of said apertures extending from the wall of said inner conductor inwardly thereof and having a terminal portion inside of said inner conductor;

and dielectric support means for maintaining said inner and outer conductors in coaxial relation;

said support means including a plurality of pins of deformable dielectric material, each said pin being disposed in and extending through a pair of said aligned apertures of said inner conductor with the ends of the pin in supporting engagement with said outer conuctor;

and said terminal portion of said aperture wall being embedded in at least one localized area in the dielectric pin disposed in that aperture so that axial movement of said pin relative to said aperture is prevented.

2. A coaxial electrical transmission line comprising a tubular outer conductor;

a tubular inner conductor coaxially disposed within said outer conductor;

said inner conductor having a plurality of pairs of opposed aligned apertures;

we wall of each of said apertures including a toroidal surface extending from the wall of said inner conductor inwardly thereof and terminating in a plurality of inwardly projecting prongs;

and dielectric support means for maintaining said inner and outer conductors in coaxial relation;

said support means including a plurality of pins of deformable dielectric material, each said pin being dis-,

posed in and extending through a pair of said aligned apertures of said inner conductor with the ends of the pin in supporting engagement with said outer conductor;

and a portion of a prong at least one of each of said pairs of apertures being embedded in at least one localized area in the dielectric pin disposed in that aperture so that axial movement of said pin relative to said aperture is prevented.

3. A coaxial electrical transmission line comprising a cylindrical outer conductor;

a cylindrical inner conductor coaxially disposed within said outer conductor;

said inner connector having a plurality of pairs of diametrically opposed aligned apertures;

the wall of each of said apertures including a toroidal surface extending from the wall of said inner conductor inwardly thereof and terminating in a plurality of inwardly projecting prongs;

and dielectric support means for maintaining said inner and outer conductors in coaxial relation;

said support means including a plurality of pins of deformable dielectric material, each said pin being disposed in and extending through a pair of said aligned apertures of said inner conductor with the ends of the pin in suporting engagement with said outer conductor;

and a portion of each of two axially opposed prongs at each of said apertures being embedded in at least one localized area in the dielectric pin disposed in that aperture so that axial movement of said pin relative to said aperture is prevented.

4. For use in coaxial electrical transmission line comprising a tubular outer conductor;

a tubular inner conductor adapted to be coaxially disposed with said outer conductor;

said inner conductor having a plurality of pairs of opposed aligned apertures therein;

the wall of each of said apertures extending from the wall of said inner conductor inwardly thereof and having a terminal portion inside of said inner conductor;

and dielectric support means for maintaining said inner and outer conductors in coaxial relation;

said support means including a plurality of pins of deformable dielectric material, each said pin being disposed in and extending through a pair of said aligned apertures of said inner conductor with the ends of 7 8 the pin adapted to be placed in supporting engage- References Cited ment with outer conductor; UNITED STATES PATENTS and said terminal porti n of said aperture wall being embedded in at least one localized area in the di- 2280200 4/1942 Smlth electric pin disposed in that aperture so that axial 5 movement of Said P mlativ to Said aperture is HERMAN KARL SAALBACH,PlzmalyExammer.

prevented. L. ALLAHUT, Assistant Examiner. 

1. A COAXIAL ELECTRICAL TRANSMISSION LINE COMPRISING A TUBULAR OUTER CONDUCTOR; A TUBULAR INNER CONDUCTOR COAXIALLY DISPOSED WITHIN SAID OUTER CONDUCTOR; SAID INNER CONDUCTOR HAVING A PLURALITY OF PAIRS OF OPPOSED ALIGNED APERTURES THEREIN; THE WALL OF EACH OF SAID APERTURES EXTENDING FROM THE WALL OF SAID INNER CONDUCTOR INWARDLY THEREOF AND HAVING A TERMINAL PORTION INSIDE OF SAID INNER CONDUCTOR; AND DIELECTRIC SUPPORT MEANS FOR MAINTAINING SAID INNER AND OUTER CONDUCTORS IN COAXIAL RELATION; SAID SUPPORT MEANS INCLUDING A PLURALITY OF PINS OF DEFORMABLE DIELECTRIC MATERIAL, EACH SAID PIN BEING DISPOSED IN AND EXTENDING THROUGH A PAIR OF SAID ALIGNED APERTURES OF SAID INNER CONDUCTOR WITH THE ENDS OF THE PIN IN SUPPORTING ENGAGEMENT WITH SAID OUTER CONDUCTOR; AND SAID TERMINAL PORTION OF SAID APERTURE WALL BEING EMBEDDED IN AT LEAST ONE LOCALIZED AREA IN THE DIELECTRIC PIN DISPOSED IN THAT APERTURE SO THAT AXIAL MOVEMENT OF SAID PIN RELATIVE TO SAID APERTURE IS PREVENTED. 